Lightning and surge protection in outdoor lighting systems

Transcription

1 Lightning and surge protection in outdoor lighting systems Cirprotec Technical Article No. 3 Page 1

2 0. Introduction The various types of voltage surges have a direct impact on public lighting systems. Both transient overvoltages and permanent overvoltages (TOV) cause premature wear of the lighting fixtures and control components as well as causing unnecessary increases in consumption, extended service interruptions and even fires. The Spanish Low Voltage Electrotechnical Regulations (R.E.B.T. 2002) reflect the vulnerability on these systems in Technical Bulletin ITC-BT-09: Outdoor lighting systems; furthermore, ITC-BT-23: Voltage Surge Protection makes it obligatory to protect systems having overhead feeds or where continuity of supply is critical. An incident caused by any type of overvoltage will damage not only the lighting fixtures and the ballasts that feed them; electrical panels for public lighting incorporate flow reduction devices, high value energy-efficient devices designed to minimise consumption and perform real-time monitoring of the operation of the fixtures. These devices are particularly susceptible to both transient and permanent overvoltages (TOV), which have quite a serious impact. In addition, this problem can lead to an uncontrolled increase in consumption, resulting in higher electricity bills. Finally, the material damage to the fixtures often leads to the actuation of cut-out devices in the electrical panel, interrupting the power supply and therefore the lighting service. So as well as the cost of repairs, users are left with no service, an issue which is always critical and may on occasions directly affect the safety of people, as in the case of tunnels and lighting inter-city road lighting and signage. This article explains what each type of overvoltage is and how to prevent them, while proposing an integrated solution for maximising protection performance and service continuity. Fig. 1 Typical diagram of a public lighting electrical control panel Page 2

3 1. What are overvoltages? When analysing the phenomenon of overvoltages, a distinction is always made between transient overvoltages and permanent overvoltages (a.k.a. TOV temporary overvoltages). Although they both represent an increase in voltage above the allowable limit, their causes, magnitude, duration and method of protection are different. Transient overvoltages are surges that can reach tens of kilovolts with a duration of the order of microseconds. Despite their short duration, the high energy content can cause serious problems to equipment connected to the line, from premature aging to destruction, causing disruptions to service and financial loss. This type of surge can have various different causes, including atmospheric lightning directly striking the external protection (lightning rods) on a building or transmission line or the associated induction of electromagnetic fields on metallic conductors. Outdoor and very long lines are the most susceptible to these fields, often receiving large induction currents. It is also common for nonweather phenomena, such as transformer centre switching or the disconnection of motors or other inductive loads to cause voltage spikes in adjacent lines. Fig. 2 Transient overvoltage Transient overvoltages are voltage spikes of tens of kilovolts with a duration of microseconds Transient overvoltage protection is achieved by installing the protector (surge arrester) on the vulnerable line, connecting it in parallel between the line and earth. This means that in the event of a transient overvoltage, the protector will discharge excess energy to earth, thus limiting the peak voltage to a value acceptable for the electrical equipment connected. Besides the phenomenon of transient overvoltages, which may affect any type of conductor, electric transmission lines can transmit a second type of overvoltage, known as permanent overvoltages (TOV). These are considered to be any voltage increase above 10% of the effective nominal value during a period of an order of seconds. Permanent overvoltages (TOV) are causes by supply problems, or, very often, by bad connections or breakage of the neutral conductor. When the latter Fig. 3 Permanent overvoltage (TOV) occurs, the single-sided voltage received by any system connected between phase and neutral is floating and depends on the imbalance of the load/charge on the three-phase network, and can supply as much as 400 effective Volts instead of the 230V expected. An increase in effective voltage can lead to the premature aging of receivers, increases in consumption or destruction, with the resulting fire risk. The protection method for this type of overvoltages consists of monitoring the voltage between each of the phases and neutral and operating a cut-out if this value rises to over 10% above nominal. Permanent overvoltages (TOV) are surges in the mains supply of hundreds of volts for an unspecified period Page 3

4 2. Regulatory framework Transient overvoltages in public lighting systems have been known about for a long time. The configuration of the system, outdoors, with long lengths of cable, leads to a high incidence of inductions produced by atmospheric phenomena. This is why the Spanish R.E.B.T deals with this problem in ITCs BT-09 and BT-23. Section 4 of ITC-BT-09 provides that: ( ) lines shall always be protected against overvoltages where the equipment installed so requires Section 3.2 of ITC-BT-23 provides that: ( ) In a controlled situation, when a system is fed by, or includes, an overhead line with bare or insulated conductors, protection against overvoltages of an atmospheric origin is considered necessary at the system's entrance. Furthermore, we must not forget the Special Technical Regulations for electricity companies, adopted by various autonomous regions such as Catalonia and more recently Aragon, which make it mandatory to protect any electricity mains system against the effects of permanent overvoltages (TOV), and Andalusia, where protection against both transient and permanent overvoltages (TOV) is obligatory on any installation. CENELEC is working on a European Standard to set the framework for protection devices against power frequency overvoltages, i.e. permanent overvoltages (TOV). 3. The problem of overvoltages in public lighting systems Flow stabilisers-reducers Flow stabilisers or reducers are voltage regulation components designed to reduce light flow at times of low use and to eliminate night-time voltage surges that cause significant increases in consumption by lamps. The growing need to adopt energy saving measures to optimise the costs of public lighting has led to the widespread introduction of flow reducers over the last few years. Both R.E.B.T. 2002, in ITC-BT-09, and the model municipal ordinance for outdoor lighting proposed by the IDAE, provide for the requirement to use systems that regulate the light level. The function of a flow stabiliser is not, however, to protect the charges it supplies from the effects of overvoltages, but to reduce the latter's supply voltage in order to optimize the electricity bill. This ability to reduce output voltage is limited to an input voltage range, which, according to the model, varies between +8% and + 10% of the nominal voltage. This means that, on a 230V supply, the stabiliser's self-protection bypass will activate on any input voltage above 255V, allowing this voltage to directly reach the lamps. Fig. 4 Commercial models of flow stabilisers-reducers Page 4

5 Reactances-ballasts Reactances or ballasts are accessories used in combination with discharge lamps, in order to ensure they function correctly. A common characteristic of discharge lamps is that they have an impedance to the passage of current which decreases as the current increases, which means they cannot be directly connected to the mains without a device, the reactance or ballast, to control the current through them. There are two quite distinct groups of reactances for discharge lamps, depending on the technology used: electromagnetic and high-frequency electronic. Deployment of electronic reactances, replacing the conventional system consisting of reactance, starter and condenser, has gradually increased over the last few years, due to its greater light efficiency, energy economy and technical advantages. However, as in all electronic equipment, these reactances are less robust than the conventional ones, a fact which should be taken into account in the design of lighting systems. This observation also extends to the mixing of technologies when lamps with electromagnetic equipment are replaced by ones with electronic systems. Current peaks caused by the charging and discharging of the condensers included in conventional equipment significantly reduce the lifetime of highfrequency equipment. The risk of deterioration is so high that most ballast manufacturers specify that the co-existence of both technologies in the same lighting circuit must be avoided at all costs. This is a difficult restriction to adhere to, however, since at the municipal level it is usual to change from one technology to the other as old components need to be replaced. Fig. 5 Commercial models of electronic ballasts Fig. 6 Conventional solution with electromagnetic ballast and condenser Page 5

6 Protection against the effects of overvoltages in public lighting Transient overvoltages: The solution is installed downstream of the control panel's circuit breaker, in parallel to the system, shunting the energy of the surge to earth and limiting the voltage peak to an acceptable value for the connected equipment. Among the various causes of surges contemplated in standard UNE-EN , the ones most likely to affect a public lighting system are those caused by direct lightning strikes near to the structure (induced) or the mains lines (conducted). Standards UNE-EN and UNE-EN require that protection against this type of electrical disturbance be provided by Type 2 protectors, tested with an 8/20 type wave. The distance between the protector and the equipment to be protected must be as short as possible to guarantee proper protection. This is why, if the distance between the protection panel and the lamps is over metres, a second protection stage of type 2 or 3, located inside the lamp, is recommended. Installation of this second level of protection also guarantees adequate protection of the remote control equipment located in it, increasingly common in today's lighting systems, in view of the increasing need to achieve energy savings. Permanent overvoltages (TOV) As already mentioned above, permanent overvoltages (TOV) can also be received through the mains supply. These exceed the nominal voltage by at least 10% and can reach values of up to 400V between phase and neutral, and, unlike transient overvoltages, are of unspecified duration. This type of overvoltage has negative effects on outdoor lighting systems: Increased system consumption: the increase in energy consumed is directly proportional to the increase in voltage. An increase in voltage of 10% can, depending on the type of lamp, result in an increase in current of up to 27%. These voltage fluctuations are very common in mains supplies, especially during the night, which is why the use of flow stabilisers-reducers in outdoor lighting control panels is becoming increasingly common. This equipment rectifies the input voltage to a constant output, although this function is limited to input voltage values of up to 10% of nominal. This implies that the stabiliser will automatically go over to bypass mode on any input voltage in excess of this range. Reduction of lamp and reactance lifetime. An increase in voltage of just 10% can lead to a 35% shortening of the lifetime of lamps and their supply reactances. This aging may be much faster, or even immediate, in the event of higher overvoltages and can cause fires. Reduction of equipment lifetime. Equipment installed in the electrical panel responsible for the measurement, astronomical management and reduction of light flow is also very sensitive to permanent overvoltages (TOV). Its high financial cost and its importance in the system make protecting it very important. Service interruption. If a permanent overvoltage (TOV) occurs, the public roadway will remain without lighting until a technician comes and repairs the equipment and the electrical panel. In tunnels and inter-urban lighting and signposting systems, lack of lighting also implies a risk to users. Proper protection against these overvoltages will act on the circuit breaker (MCB) or on the main contactor switch on the lighting panel before any receiver suffers any damage. In this way, not only the lamps, but the costly equipment installed in the panel will also be protected. Furthermore, latest-technology protectors provide safe automatic reconnection. As soon as the voltage returns to a safe value, the protector will automatically reconnect, minimising down time and saving travel costs of maintenance personnel. Page 6

7 4. Cirprotec solutions Due to the need to protect public lighting systems from the impact of transient and permanent overvoltages (TOV), Cirprotec has developed the V-Check range, to provide combined protection against both types of overvoltage in a single product. Public lighting control panels up to 63A The V-Check 4MR solution is installed on a DIN rail, occupying a space of 5 modules plus the 4 modules occupied by the built-in I.G.A. (9 modules in total). V-Check provides short-circuit and overcurrent protection via the incorporated MCB (available for various current levels), protection against transient and permanent overvoltages (TOV) with automatic reconnection. Fig.7 Complete public lighting system with V-Check 4MR Providing the combined protection of V-Check 4MR, both the lamps and the lighting panel equipment will be protected against transient and permanent overvoltages (TOV), minimising down time, thanks to safe, automatic reconnection. Page 7

8 Public lighting control panels over 63A The V-Check 4RC solution is installed on a DIN rail, occupying a space of 4 modules. The V-Check provides protection against transient and permanent overvoltages (TOV) with automatic reconnection via actuation on the main contactor switch by means of a volt-free contact. Fig.8 Complete public lighting system with V-Check 4RC Providing combined protection of V-Check 4RC, both the lamps and the lighting panel equipment will be protected against transient and permanent overvoltages (TOV), minimising down time, thanks to safe, automatic reconnection. As far as protection against permanent overvoltages (TOV) is concerned, both protectors have tripping curves in conformance with European standards. These curves have two aims: to avoid untimely tripping with small increases in voltage due to mains load variations and, above all, and very importantly, to ensure rapid actuation in the event of high overvoltages (<350V), since at this overvoltage level destruction of equipment is almost immediate. In addition to the protection against transient overvoltages included in these protectors, Cirprotec recommends the installation of a second Type 2 transient overvoltage protector in series located inside the lamp, in order to guarantee proper protection at the points furthest away from the lighting panel. Page 8

9 The Cirprotec Technical Articles Collection 1. - Lightning and surge protection in TDT signal repeaters and Gap fillers Overvoltage and surge protection in common telecommunications systems in buildings. 3.- Lightning and surge protection in outdoor lighting systems Lightning and surge protection in schools Lightning and surge protection in waste water purification plants Lightning and surge protection in the AHIS (Automatic Hydrological Information System) network Lightning and surge protection in BANKING PREMISES 8.- Power frequency overvoltage. EN50550 standard Power Frequency Overvoltage Protectors (POP) Page 9